The invention relates to a device for aligning sheets laterally, in particular, in the feeder of a sheet-processing machine.
In order to feed a sheet with proper alignment to a sheet-processing machine, for example, a printing machine, it is necessary to align the sheet in the circumferential direction at so-called front guides or lays and to align it laterally at so-called side stops. For this purpose, the sheet is conveyed against the front guides by a suitable transporter, and is drawn against the side stops by a so-called side pulling device.
The German Patent 972 459, for example, discloses the use of a suction pull rail, which sucks the sheet from below by a suction nozzle and conveys the sheet against a side stop. To prevent the sheet from escaping upwardly when it impacts the side stop, a hold-down plate is provided in order to hold the sheet down on the feed table.
Such hold-down plates, however, have the disadvantage that a sheet which is aligned in the leading region thereof as it is conveyed into the sheet-processing machine must also be conveyed through, under the down-holder at the trailing end thereof. Extremely small skewed sheet positions or skewed sections lead to sheet warping at the side stops and the down-holder, respectively. If a sheet is drawn into the printing unit in a warped condition, however, this has a detrimental effect upon the feed register and upon ghosting caused by the feeder.
It is accordingly an object of the invention to provide a device for aligning sheets laterally which manages without a down-holder in the region of the side stops.
With the foregoing and other objects in view, there is provided, in accordance with one aspect of the invention, a device for aligning sheets laterally on a feed table of a sheet-processing machine, having a side stop, comprising a suction pull nozzle movable transversely to a sheet transport direction and being formed with a plurality of suction openings, the suction openings being distributed so that the number of suction openings arranged in the sheet transport direction becomes greater in a transverse direction towards the side stop.
In accordance with another feature of the invention, the suction openings are formed as suction bores.
In accordance with a further feature of the invention, the suction bores have greater diameters in the direction towards the side stop than towards a center of the feed table.
In accordance with an added feature of the invention, the suction openings are distributed in the form of a triangle.
In accordance with an additional feature of the invention, the suction openings are distributed in the form of a semicircle.
In accordance with yet another feature of the invention, the aligning device includes a suction chamber for supplying vacuum to the suction bores, the suction chamber being divided into two subchambers in the transverse direction, the suction chamber being constructed so as to be disconnectable.
In accordance with yet a further feature of the invention, the aligning device includes a slide operatable in an infinitely variable manner in the transverse direction for closing the suction bores.
In accordance with another aspect of the invention, there is provided a device for aligning sheets laterally on a feed table of a sheet-processing machine, having a suction pull nozzle movable transversely to a sheet transport direction and having a plurality of suction openings, comprising a side stop formed with a slope extending in a direction of a sheet lateral edge.
In accordance with an added feature of the invention, an imaginary extension of the slope forms an acute angle with a transport plane of the feed table.
In accordance with a third aspect of the invention, there is provided a device for aligning sheets laterally on a feed table of a sheet-processing machine, having a side stop and a suction pull nozzle movable transversely to a sheet transport direction, and being formed with a plurality of suction openings, comprising a run-on slope formed on the side stop, the run-on slope being oriented counter to the sheet transport direction.
In accordance with another feature of the invention, the run-on slope forms an acute angle with a sheet guide plane.
In accordance with a concomitant feature of the invention, the run-on slope is constructed so as to extend below a sheet guide plane.
A particular advantage of the invention is that a suction force acting on the sheet through the suction nozzle is distributed over suction openings in such a way that the number of suction openings in the sheet transport direction is higher than in the transverse direction, or is at least equally high. The sheet to be transported is thereby held securely by the suction nozzle, with a small total holding force, in particular in the edge region of the sheet. Due to this measure, the sheet is able to execute a relative movement with respect to the suction nozzle the instant the side edge of the sheet contacts the side stop, so that the edge is not damaged. The distribution of the suction force in accordance with the invention, a greater suction force being provided in the edge region of the sheet, causes the edge of the sheet not to wander upwardly, even when it strikes the side stop. Therefore, down-holders in the region of the side stops can be dispensed with.
Dispensing with down-holders makes it possible for the sheet that is transported away to slide over the side stops in order to relieve stress. Run-on slopes advantageously arranged on the side stops assist this measure.
Moreover, a further run-on slope directed counter to the sheet transport direction is provided on the side stop, and makes it possible for a laterally, negatively offset oncoming sheet not to be caught or remain hanging on the side stop but to slide over the latter. In order to rule out the possibility of the side stop being a stumbling block, the run-on slope is formed to-extend below the sheet guide plane.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a device for aligning sheets laterally, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings, wherein: